Reinforced abrasive wheel



' Feb. 20, 1945.

A. 1.. [BALL ET AL Filed May 22, 1944 REINFORCED ABRASIVE WHEEL 2Sheets-Sheet l N m I a k s: i E\\\ I $3 m l INVENTORS. ALBfET L. BALL YP2550077- h. NAM/(5e Feb. 20, 1945. A, L BALL ET AL 2,369,639-

REINFORCED ABRAS IVE WHEEL Filed May 22, 1944 2 Sheets-Sheet 2INVENTORS' AL 556 T A. BHL L Patented Feb. 20, 1945 REINFORCED ABRASIVEWHEEL Albert L. Ball, Lewiston, and Prescott H. Walker, Niagara Falls,N. Y., assignors to The Carborundum Company, Niagara Falls, N. Y., acorporation of Delaware Application May 22, 1944, Serial No. 536,708

15 Claims.

This invention relates to reinforced abrasive wheels and particularly tolarge diameter abrasive wheels suchas those employed in the manufactureof wood pulp.

One of the objects of the invention is to pro vide a large diameterwheel so reinforced against centrifugal force and the forces set up bythermal expansion that the abrasive rim can be made in the form of aunitary annulus. Such unitary abrasive structure presents numerousadvantages, among the most salient of which are ease of manufacture andthe uniformity of grinding action. Although the wheel of the presentin-- vention is use-d advantageously as a pulp wheel, it can also beused to advantage in other applications requiring a large diameterwheel, and presents particular advantages where such wheel is subjectedto severe stresses resulting from centrifugal force, the tangentialforce resulting from the grinding load, and expansive forces resultingfrom local and over-all heating of the abrasive structure.

The wheel of the present invention will, for ease of understanding theinvention, be described in connection with its use as a pulp wheel. Inthe production of wood pulp by the conventional grinding method it isnecessary to provide a very large and strong abrasive wheel, since largeand heavy logs are thrust with great force against the wheel therebyproducing enormous grinding forces. -Pulp wheels are conventionally 5feet or more in diameter and weigh as much as eight tons. The logs beingground are forced against the face of the wheel under very heavypressure, so great in fact, that as much as 1500 H. P. or more. isrequired to revolve the wheels at approximately 250 R. P. M. Thus thestructure of the wheel must be such that it will with- I stand thecentrifugal force resulting from its great weight and the relativelyhigh surface speed of the abrasive, and also withstand the inward thrustapplied by the logs being ground, and the tangential force required tomove-the wheel past the work.

In addition to these forces the pulp wheel is subjected to relativelyhigh temperatures during use, since besides the local heating developedby reason of the contact of the wheel with the logs, which may reach ashigh as 400 F., the wheel operates in a pit at least partially filledwith hot water which ma reach a temperature of 212 F. Such hot water isnecessary in order to provide the necessary loosening of the fibers tornfrom the logs by the grinding wheel.

Although one piece, or monolithic, pulp wheels have been described inthe prior art and attempts have been made to reinforce such wheels inorder to enable them to stand up under severe operating conditions, pulpwheels'which are now almost universally'in use consist of abrasivesegments anchored to a drum. In order to compensate for the thermalexpansion of individual segments and to seal the abrasive structureagainst the influx of water, thin packing members are generally employedbetween segments, such packings being in the nature of rubber orrubber-like materials employing fillers and the like. The use of largesegmental type wheels has long been recognized as presenting numerousdisadvantages. Their construction involves the assembly of a, largenumber of parts, all of which must be very carefully put in place if thestructure is to be safe. The packings employed between segmentsfrequently give trouble by wearing away much'faster than the abrasiveand by being attacked by the hot water. Becaus the abrading surface ofthe wheels is not continuous, but is broken up :into a large number ofsegments, the grinding action, whether upon wood Or any other material,is uneven, since a different type of product is produced every time ajoint passes the material being ground from what is produced when otherportions of the abrasive rim traverse the work. In the case of pulpwheels such joints cause the production of a relatively large amount ofcoarse waste pulp. In spite of these disadvantages of segmental wheels,which are well-known, and in spite of the fact that the grinding actionof a one-piece abrasive annulus has long been recognized as the idealone, pulp wheels of segmental abrasive construction were almostuniversally employed before the present invention. This was due to theimpossibility of producing large wheels with one piece abrasive, rimswhich would stand up under the grinding conditions imposed, particularlythose encountered in wood pulp grinding.

The present invention makes feasible the use of a one piece abrasiveannulus of the diameter desired, which may be in the order of 5 feet,and may reach '72 inches or above. The abrasive annulus, which isrelatively thin in a radial direction compared to its total diameter, isprovided with a supporting and driving means, such means being soconstructed that it subjects the abrasive annulus to a predeterminedcompressive or inwardly directed force so that the abrasive is under alarge yet permissible compressive stress circumferentially when thewheel is at room temperature and not rotating, said force being subthabrasive rim, the normal speed of rotation of the wheel, and the averagetemperature of the wet pulp bath in which it operates under normalconditions, so that during normal operation the abrasive rim will be inits normal, relatively unstressed condition or under a relatively smallcompressive force and able to stand up under operating grinding loadsand local and over-all temperature changes.

The inventionv will be more readily understood by reference to theaccompanying drawings in which,

Figure l is a side elevation of a partially constructed wheel made inaccordance with the present invention,

Figure 2 is a view in cross section taken along the line 22 in Figure 1,

Figure 3 is a perspective view of a completed wheel employing a singleunitary abrasive annulus, and,

Figure 4 is a perspective view of a completed wheel employing twoabrasive annuli mounted side by side.

In Figure 1, the abrasive portion.of the wheel consists of a unitaryabrasive annulus I of known pulp wheel composition. The annulus is madeby pressing a mixture of abrasive grain and ceramic bond, drying thestructure, and firing to vitrify the bond. A softer grade abrasive maybe employed in the wheel of this invention than is feasible where theabrasive is in segments, since in the latter construction if thesegments were too soft the entering edge of each segment, being adjacenta relatively soft separator layer, would be worn down much more rapidlythan the remainder of the segment. Abrasive annulus l is provided with aplurality of radial slots 2 which extend from the inner surface of theannulus to points a substantial distance from the outer periphery. InFigure 1 such distance is roughly be tween and the radial thickness ofthe annulus. Slots 2 connect with bores 3 (Fig. 2), which may beapproximately cylindrical and which extend a substantial distance intothe abrasive rim in an angular direction toward the axis of the annulus.Slots 2 and bores 3 may be formed by suitably shaped core members on thetop and bottom plates of the mold during pressing of the annulus, suchcore members being withdrawn either manually or mechanically aftermolding in such direction as not to deform or break out the moldedstructure around them. The abrasive rim may be solid throughout itsextent with the exception of slots 2 and bores 3, or may be provided, atlocations substantially intermediate bores 3, with shallow radiallydirected slots 4 to allow the inner periphery of the annulus to assumemore readily a smaller diameter when the annulus is subjected toinwardly directed tension. Slots 4 may, in the finished annulus, befilled with a resilient material such as soft rubber or the like.

The rim supporting and driving means is now assembled with the abrasiveannulus. This is done by inserting the short end 5 of a hook shapedspo'ke 6 into each bore 3 in the rim, locating it axially and in aradial direction with reference to the adjacent side of the abrasive rimby means of a suitable jig, and then pouring about the inserted shortend of the spoke a suit able, hardenable seating material 1. One suchsuitable seating material is Babbitt metal, which is fusible at suchtemperatures that it may be poured into the abrasive without crackingit, and which, when it hardens, becomes suitably rigid and resistant toflow to provide an unyielding seat for the short end of the spoke. Spoke6 may be made in one piece of a suitable high strength but elasticmetal, such as high strength ironnickel alloy having a coefiicient ofexpansion approximating that of the abrasive rim. Alternatively, thespokes may be made with the portion containing short end 5 and asuitable length of the shank of one metal or alloy and the remainder ofthe shank of another metal or alloy, the two portions being connected asby a screw threaded coupling or being integrally joined as by welding.Such composite spoke structure may be made more accurately to conform tothe thermal coefficient of expansion of the assembled wheel structure asa Whole.

After the spokes have been assembled in the abrasive rim and seatingmaterial I has been poured about the short end of each, a metal ring orannulus 8 of metal having such depth of section that it has sufficientstrength in a radial direction to withstand the force imposed, is placedbetween the shanks of opposite spokes 6, in a position coaxial with theaxis of the rim. Metal straps 9, having a length approximately equal tothe width of the rim, and having a hole I 0 at each end so spaced as toreceive the shanks of the opposed pairs of spokes, are then assembledand are held in place by means of nuts II screwed onto the threaded endsI2 of the long shanks of the spokes. Various nuts II are tightenedprogressively in a predetermined order and to a gradually increasingtension so that metal ring 8 is coaxial of the rim at all times. Thefinal predetermined tension to be given to each spoke may then beapplied by means of a calibrated wrench with which nuts II are finallytightened. Such final tension, as has been explained above, issubstantially one such that centrifugal force and normal heat expansionforces will approximately balance such tension when the wheel is inoperation. It may be preferred, however, to impose a slightly higherinitial tension in spokes B so that under normal operating conditionsthe abrasive rim will always be subjected to circumferentialcompression. The tension is such that it and any higher tension inspokes 6 arising from operation of the wheel will lie well within theelastic limit of the material of which the hooks are made.

The pre-stressing of the abrasive rim above set out may be accomplishedwhile all parts of the wheel are at room temperature. Alternatively.metal rim 8 may be heated to a predetermined temperature beforeassembly, in which case nuts I I are tightened to a somewhat lowerdegree, additional pro-stressing being furnished by ring 8 upon itscooling to room temperature. A converse of this method, which may alsobe used, leaves metal ring 8 at room temperature and cools the abrasiverim section as by being placed in contact with dry ice.

Although hook shaped spokes have been shown as the means connecting thewheel supporting and driving means with the abrasive rim, it is to beunderstood that other types of tensioning members firmly secured to theabrasive annulus may be'employed. One such means consists of nutsembedded in radial bores in the abrasive and secured therein by castmetal or cement, and radially directed bolts screwed into the nuts toact as spokes in the finished wheel. In wheels employed if such meansare located centrally of the rim and-are such as to exert a force on therim in a purely radial direction. However, it

i usually preferred to use at least two rows of such members, locatedadjacent opposite sides of the rim, as shown in Figures 1 and 2. It isconvenient although not necessary, to have members of opposite rows formopposed pairs. The construction should, however, be such that iteffectively balances the forces applied to the abrasive portion andyields a balanced, stable, wheel construction. It is obvious, in eitherconstruction described above, to employ a central spoke securing meansother than annular in shape and to use means other than the strapsdescribed for securing the spokes to such member.

After the structure shown in Figure 1 has been completelyassembled, andthe abrasive rim subjected to the predetermined degree of inward forceexerted by spokes 6 or the equivalent means above described, the spacebetween the abrasive rim l and the metal ring 8 and the space inwardlyof ring 8 up to the central arbor hole in the wheel is filled withconcrete to produce the structure shown in Figure 3. The location of thearbor hole is indicated by a dotted circle I3 in Figure 1 and by dottedlines M in Figure 2. Slots 2 are likewise filled with concrete and thefinished structure is, in the modification shown, brought to a finalthickness equal to that of the abrasive rim. In order to produce thecentral arbor hole in the wheel, a removable form is employed which ispositioned coaxially of the wheel,'during pouring and hardening of theconcrete, such form having a configuration on its outer surfacecorresponding to theshape of the arbor hole desired. Reinforcing metalring members l5, of which one is shown in Figure 3, are located in thecenter of the wheel by the arbor hole forming means and becomeincorporated in the wheel as a permanent part thereof after the concretehas hardened and the arbor hole forming means is removed. A wheelsupporting and driving arbor 16 extends through the arbor hole in thewheel and interfits with the members IS in the wheel by means ofbushings ll, of which one is partially shown in Figure 3, which fit inbetween arbor l6 and metal reinforcing rings within close tolerances.The wheel is held against movement axially of the arbor and is driven bymeans of flanges (not shown) which are screwed onto threaded portions l8of the arbor, one on each side of the wheel. The threads on each ofthe-portions I8 are made of such hand that the flanges on both sides ofthe wheel tend to tighten against the wheel as the'wheel is driven.

Although the structure shown in Figure 3 is suitable for manyapplications, it is preferable in some cases, particularly where widerwheels are desired than are feasible to make in one piece, to use acomposite wheel such as that constructed in Figure 4. Such wheel is madeby forming two similar abrasive annuli, similar to thoseshown as l inFigures 1 and 2, mounting spokes or equivalent means in each annulus forexerting tension inwardly of the annulus, placing the annuli together ina coaxial position with the anchor hooks aligned, and positioning ametal ring such as ring 8 shown imFiguresi and 2 within each of theabrasive annuli: Strap members designated l9 are employed in this "case,such members being of substantially the same width as the two assembledannuli so that the inner ends of four aligned spokes, two for eachannulus, project through each one. The annuli are subjected to apredetermined amount of stress directed inwardly by the same methods orcombinations of methods disclosed in connection with the modificationsshown in Figures 1 and 2.

It is preferable, in making a wheel such as shown in Figure 4, to employbiased joints between adjacent annuli. This may be accomplished bydressing the adjacent sides of the two or more annuli so that theyinterfit but so that the joint does not lie in a radial plane, that is,a plane at right angles to the axis of the wheel. In a pulp wheel it issuflicient that the joint or joints lie in a plane but that at one pointon the circumference of the wheel it lies from to 1 on one side of aradial plane and at a point 180 removed from the first named point itlies from to 1" on the other side of the same radial plane. Such abiased jointprevents the production of the coarse waste pulp which wouldresult at the joint if it lay in a radial plane.

It is possible, in thus making a composite wheel, to place the abrasiveannuli directly in contact with each other, but it is preferred, inorder to minimize stresses arising from thermal expansion and also inorder to seal the joint between annuli, to employ a packing material 20between them. Such packing is shown, for v harden the synthetic resin inthe outer layers of fabric and to vulcanize the intermediate rubbercomposition. A sufiicient number of layered sheets made in a mannersimilar to that just described are placed between the abrasive annuli toroduce packing layer 20. Instead of having the layered sheets contactwith the surfaces of the abrasive annuli, a self-hardening resinouscement can be used in direct contact with the annuli, and one or more ofthe layered sheets of the kind described above used to complete thejoint between the abrasive annuli.

The wheel in Figure 4 has concrete poured into its center portion bothbetween the abrasive annuli and the inner metal rings, and between themetal rings and the central arbor hole. The Wheel likewise is providedwith reinforcing metal rings [5 permanently incorporated into the arborhole, and is mounted on an arbor I6 by means of bushings I'I between thearbor and rings [5 and by means of suitable flanges (not shown) screwedonto threaded portions of the arbor. Although the wheel shown in Figure4 'has but two annuli l involved in its make-up, it is obvious thatwider abrasive wheels can be made employing as many annuli as desiredplaced side by side and connected together in the same manner as inFigure 4.

Although the invention has been described in connection with thespecific structures shown and it has been discussed in connection withits use as a pulp wheel, it is to be understood that the invention maybe used in structures equivalent to those described, and that itdisplays advantages in other applications where large diameter wheelsare employed in rigorous grinding opera tions. Other advantages of theinvention besides those above pointed out will be apparent to thoseskilled in the art from the foregoing description taken in connectionwith the drawings. The invention is therefore defined within the compassof the following claims:

We claim:

1. A reinforced abrasive wheel comprising an integral abrasive annulusof relatively large diameter, said annulus being relatively thin in aradial direction as compared to its total radius, said annulus beingprovided with a plurality of pairs of opposed radial slots on the sidesthereof extending from the inner circumference of the abrasive annulusfor a substantial distance toward the outer circumference thereof, saidslots being spaced equally about the abrasive annulus, there being aninwardly directed bore connecting tothe outermost portion of each slot,said bore being of substantial depth and being directed angularly towardthe axis of the annulus, said annulus being provided with a plurality ofspokes having long and short portions directed at an acute angle to eachother, the short end of each of said spokes being each inserted into oneof the angularly directed bores in the annulus and being fitted and heldtherein by means of a hardened cast metal seat, the long ends of thespokes being threaded and being directed radially of the abrasive rim,the outer parts of the long ends being received in the radial slots inthe abrasive annulus, a strong metal annulus of substantially smallerdiameter than that of the abrasive annulus and of such width as to fitsnugly between the long portions of opposed pairs of spokes, said metalannulus being located coaxially of the abrasive rim, a plurality ofstrap members, each having a hole at each end thereof and so spaced asto fit over the long ends of two opposed spoke members, said strapsbeing positioned parallel to the axis of the metal annulus and incontact with the inner face thereof, and a nut on the threaded end ofeach long portion of the spokes, each nut being tightened to such anextent that all spokes are under substantially the same heavy tensilestress, the combined stresses in all spokes being such as to subject theannular abrasive rim to heavy compressive forces in a circumferentialdirection when the wheel is at rest and at room temperature, the spacebetween the abrasive annulus and the inner metal annulus and between theinner metal annulus and the arbor hole of the wheel being filled withsolidified concrete.

2. A reinforced abrasive wheel comprising an integral abrasive annulusof relatively large diameter, said annulus being relatively thin in aradial direction as compared to its total radius, said annulus beingprovided with a plurality of pairs of opposed inwardly directed bores,said bores being spaced equally about the abrasive annulus, each of saidbores being of substantial depth and being directed angularly toward theaxis of the annulus, said annulusbeing provided with a plurality ofspokes having long and short port-ions directed at an acute angle towardeach other, the short end of each of said spokes being each insertedinto one of the angularly directed bores in the annulus and being fittedand held therein by means of a hardened cast metal seat, the long endsof the spokes being threaded and being directed radially of the abrasiverim, a

strong metal annulus of such diameter and width as to fit between thelong portions of opposed pairs of spokes, said metal annulus beinglocated coaxially of the abrasive rim, a plurality of strap members,each having a hole at each end thereof and so spaced as to fit over thelong ends of two opposed spoke members, said straps being positionedparallel to the axis of the metal annulus and in contact with the innerface thereof, and a nut on the threaded end of each long portion of thespokes, each nut being tightened to such an extent that all spokes areunder substantially the same heavy tensile stress, the combined stressesin all spokes being such as to subject the annular abrasive rim tocompressive forces in a circumferential direction when the wheel is atrest and at room temperature, the space between the abrasive annulus andthe inner metal annulus and between the inner metal annulus and thearbor hole of the wheel, being filled with solidified concrete.

3. A reinforced abrasive wheel comprising an integral abrasive annulusof relatively large diameter, said annulus being relatively thin in aradial direction as compared to its total radius, said annulus beingprovided with a plurality of pairs of opposed inwardly directed bores ofsubstantial depth and directed angularly toward the axis of the annulus,said bores being spaced substantially equally about the abrasiveannulus, said annulus being provided with a plurality of spokes havinglong and short portions directed at an acute angle to each other, theshort end of each of said spokes being inserted into one of theangularly directed bores in the annulus, the long ends of the spokesbeing threaded and being directed radially of the abrasive rim, a strongmetal annulus oflsuch diameter and width as to fit between the longportions of opposed pairs of spokes, said metal annulus being locatedcoaxially of the abrasive rim, a plurality of strap members each havinga hole at each end thereof so spaced as to fit over the long ends of twoopposed spoke members, said straps being in contact with the inner faceof the metal an nulus and a nut on the threaded end of each long portionof the spokes, each nut being tightened to such an extent that allspokes are under substantially the same heavy tensile stress, wherebythe spokes subject the annular abrasive rim to compressive forces in acircumferential direction when the wheel is at rest and at roomtemperature.

4. A reinforced abrasive wheel comprising an integral abrasive annulusof relatively large diameter, said annulus being relatively thin in aradial direction as compared toits total radius,

- said annulus being provided on each side thereof with a plurality ofinwardly directed bores, the bores on each side .of the annulus beingspaced substantially equally about the annulus, the bores being ofsubstantial depth'and being directed angularly toward the axis of theannulus, said annulus being provided with a plurality of spokes havinglong and short portions directed at an acute angle to each other, theshort end of each of said spokes being inserted in one of the angularlydirected bores in the annulus, the long ends of the spokes beingthreaded and being directed radially of the abrasive rim, a strong metalannulus of such diameter and width as to fit between the long portionsof the spokes on opposite sides of the annulus, said metal annulus beinglocated coaxially of the abrasive rim and means attaching the long endsof the spokes to the metal annulus, said means comprising a nut on thelong end of each spoke, each nut being tightened to such an extent thatall spokes are under substantially the same heavy tensile stress, saidspokes subjecting the annular abrasive him to heavy-compressive forcesin a circumferential direction when the wheel is at rest and at roomtemperature.

5. 'A reinforced abrasive wheel comprising an integral abrasive annulusof relatively large diameter, said annulus being provided adjacent eachside thereof with a plurality of radially directed spokes firmlyengaging the abrasive rim, the spokes on each side of the annulus beingspaced substantially equally about the abrasive annulus, a strong metalannulus of such diameter and width as to fit between the spokes ofopposite sides of the abrasive rim, said metal annulus being locatedcoaxially of the abrasive rim, and means comprising a nut on the innerthreaded end of each spoke connecting each spoke to the metal annulus,each nut being tightened to such an extent that all spokes are under thesame tensile stress, said spokes subjecting the annular abrasive rim toheavy compressive forces in a circumferential direction when the wheelis at rest and'at room temperature.

6. A reinforced abrasive wheel comprising an integral abrasive annulusof relatively large diameter, said annulus being provided with at leastone set of radially directed spokes which lie substantially in a plane,said spokes being distributed substantially equally about the abrasiveannulus, spoke holding means within the abrasive annulus substantiallycoaxial with the abrasive annulus and means connecting each of thespokes to such spoke holding means, the means connecting each spoke tothe spoke holding means being adjustable so that each spoke may besubjected to a predetermined amount of tension, each spoke in the wheelbeing subjected to substantially the same heavy tensile stress, thespokes subjecting the annular abrasive rim to heavy compressive forcesin a circumferential direction when the wheel is at rest and at roomtemperature.

7. A reinforced abrasive wheel comprising an integral abrasive annulusof relatively large diameter, said annulus being provided with at leastone set of spokes which lie substantially in a plane, said spokes beingdistributed substantially equally about the abrasive annulus, spokeholding means within the abrasive annulus substantially coaxial with theabrasive annulus and means connecting each of the spokes to such spokeholding means, the means connecting each spoke to the spoke holdingmeans being adjustable so that each spoke may be subjected to apredetermined.

amount of tension, each spoke in the wheel being subjected tosubstantially the same heavy tensile stress, the spokes subjecting theannular abrasive rim to heavy compressive forces in a circumferentialdirection when the wheel is at rest or at room temperature.

8. A reinforced abrasive wheel comprising an integral abrasive annulus,said annulus being provided with at least one set of spokes which liesubstantially in a plane, said spokes being firmly attached to theabrasive annulus and being distributed substantially equally about theannulus, spoke holding means within the annulus, and means connectingeach of the spokes to such spoke holding means, the means connectingeach spoke to the spoke holding means being adjustable so that eachspoke may be subjected to a predetermined amount of tension, each spokein the wheel being subjected to substantially the same heavy tensilestress, the spokes subjecting the abrasive annulus to heavy compressiveforces in a circumferential direction when the wheel is at rest and atroom temperature.

9. A reinforced abrasive wheel comprising an integral abrasive annulus,said annulus being provided with at least one set of spokes, said spokesbeing firmly attached to the abrasive annulus and being distributedsubstantially equally about the annulus, spoke holding means within theannulus, each of said spokes being connected to the spoke holding meansin such manner as to be subjected to a heavy tensile stress, the spokessubjecting the abrasive annulus to heavy compressive forces in acircumferential direction.

10. A reinforced abrasive wheel comprising an integral abrasive annulus,said annulus being provided with at least one set of spokes, said spokesbeing firmly attached to the abrasive annulus and being distributedsubstantially equally about the annulus, spoke holding means within theannulus, each of said spokes being connected to the said spoke holdingmeans in such manner as to be subjected to a heavy tensile stress, thespokes subjecting the abrasive annulus to heavy compressive forces in acircumferential direction, said abrasive annulus having stress relievingslots of appreciable depth in the inner circumferential surface thereof.

11. A reinforced abrasive wheel comprising at least two integralabrasive annuli of substantially the same diameter positioned coaxially,each annulus being provided with at least one set of spokes, spokes ofadjacent annuli forming opposed pairs, said spokes being firmly attachedto the abrasive annuli and being distributed substantially equally aboutthe annuli, spoke holding means within. each annulus, each of the spokesbeing connected to a spoke holding means so as to be subjected to aheavy tensile stress, opposed pairs of spokes being held by a commonmeans holding the annuli together, the spokes subjecting'each abrasiveannulus to heavy compressive forces in a circumferential direction.

12. A reinforced abrasive wheel comprising at least two integralabrasive annuli of relatively large diameters, said annuli being ofsubstantially the same diameter and being positioned substantiallycoaxially, each annulus being provided with at least one set of spokeswhich lie substantially in a plane, spokes of adjacent annuli formingopposed pairs, said spokes being firmly attached to the abrasive annuliand being distributed substantially equally about the annuli, spokeholding means within the annuli substantially coaxial thereof, and meanscommon to opposed pairs of spokes of adjacent annuli connecting each ofthe spokes to the spoke holding means. the last named means connectingadannulus being spaced substantially equally about the abrasive annulus,the spokes in each annulus forming opposed pairs, said pairs beingaligned with similar pairs in the adjacent annulus, a strong metalannulus in each abrasive annulus, said metal annuli being of suchdiameter and width as to fit between the spokes on opposite sides of theabrasive rim, each metal annulus being located coaxially of its abrasiveannulus, elongated metal members having holes therein for the receptionof aligned spokes within the metal annuli and fitting over the innerends of aligned spokes, and'means holding the elongated metal member oneach spoke, said means being adjustable whereby the spokes may be,

tightened, each spoke being tightened to substantially the same amount,said spokes subjecting the abrasive annuli to heavy substantiallyuniform compressive forces in a circumferential direction.

14. A reinforced abrasive wheel comprising,

in combination an integral abrasive annulus, at least one pair of spokesfor the annulus, means firmly attaching the spokes to the annulus insubstantially even distribution around the an-- nulus, spoke holdingmeans within, and spaced from, the inner face of the annulus, and meansdetachably connecting each spoke to the spoke ALBERT L. BALL. PRESCOTTH. WALKER.

